MAP Technical Reports Series No. 106 UNEP

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poisoning. Prorocentrum minimum Schiller, probably responsible for the shellfish poisoning in
Norwegian coasts, is a phytoplanktonic species so common that, if it is the source of the highly
toxic "venerupin", toxin must be only in rare strains (Tangen, 1983).
7.3.1.2 Research on the components of venerupin poisoning
The toxic principles were found in the digestive glands (hepatopancreas, liver or dark
gland) of the bivalves (Akiba and Hattori, 1949). Toxicity of 75% methanol extracts of cultured
Prorocentrum minimum var. mariae-lebouriae, which is supposed to produce venerupin
poisoning (Okaichi and Imatomi, 1979) was determined using mice as test animals. The
chemical nature of the toxins is not established. The toxin was found to be soluble in water,
methanol, acetone and acetic acid. It was insoluble in benzene, ether and absolute alcohol.
7.3.1.3 Prorocentrum minimum and venerupin occurrence worldwide
Venerupin poisoning was first reported in Nagai, Japan, in 1889, following the ingestion
of the oyster Crassostrea gigas. Of the 81 persons poisoned, 51 died (Halstead, 1965). A
second outbreak occurred in 1941, when of 6 patients, 5 died, and from 1942 to 1950 there were
455 additional cases involving the eating of oysters and the short-necked clam Tapes japonica
(Nakajima, 1965). Several hundred cases have been reported in the area of Lake Hamana with
more than 100 deaths (Nakajima, 1968). So also in Norway symptoms of venerupin poisoning
have been described in 70 persons after consumption of mussels collected close to the centre
of the massive bloom of P. minimum in the autumn 1979 (Tangen, 1983).
Prorocentrum minimum Schiller red waters have often been observed in Obidos
Lagoon (Portugal) and have caused toxicity of bivalves there. Particular attention is given to two
of those blooms, separated by about 10 years, in May-June 1973 and in January-February 1983
(Silva, 1985). A comparative study of environmental conditions during the two red water of P.
minimum indicates that the instances of P. minimum red water in 1973 and 1982-83 were both
preceded by long periods of heavy rain. Phosphate in the lagoon waters increased during the
observed phytoplankton blooms, with the two maximum peaks found during the P. minimum
bloom. Also nitrate and ammonium proved to be important for the start of P. minimum growth
in 1982-83. The sudden occurrence and massive blooming of P. minimum also in Kiel Fjord on
the Baltic sea in 1983 can serve as a case study of typical coastal eutrophication (Kimor et al.,
1985). This species was previously recorded in Oslo Fjord in 1979 (Tangen, 1980), and in
subsequent years it expanded its area of distribution throughout the Skagerrak and Kattegat into
Danish and Swedish coastal waters under conditions of intense eutrophication (Granéli et al.,
1983). This was the first record of P. minimum in Kiel Fjord, and it fits well with the progressively
eastward expansion of this euryhaline and eurythermal species into the Baltic sea. The
development of the bloom was enhanced by favourable weather conditions, unusually high
temperatures of the water (> 20°C) and prevailing winds as well as by high levels of phosphate-
P and nitrate-N compounds. While the phosphate was derived mainly from anoxic sediments,
the nitrate was delivered from river runoff and originated from agricultural fertilizers.
A number of papers (Bodeanu and Usurelu, 1979; Mihnea, 1979, 1992; Petrova-
Karadzhova, 1984, 1985, 1986; Bodeanu, 1992) reported frequent summer blooms in the Black
sea, the main cause of which was held to be Exuviaella cordata (similar to the P. minimum from
Sibenik Bay in the Adriatic sea). These summer blooms were due to progressive eutrophication
of the Black sea during the seventies and eighties of this century.